Direction indicator



Feb. 27, 1940. c, QTTO' JR I 2,192,148

DIRECTION INDICATOR Filed Nov. 6, 1935 3 Sheets-Sheet 1 INVENTOR BY Car] L- Uf/QJI ATTORNEY 'Feb. 27, 1940. Q OTTO ,JR

DIRECTION INDICATQR Filed Nov. 6,1935 5 Sheets-Sheet 2 INVENTOR CarZL. U/fa, Jr.

"AT-TORNEY Feb. 27, 1940. c, QTTQ' JR I 2,192,148

DIRECTION INDICATOR v Filed Nov. 6, 1955 3 Sheets-Sheet 3 INVENTOR BY Ear/ L- U/j J;

A'IITORNEY Feb-1 21, 19

maac'rrou INDICA O f w cumin, west ne 'p'steaayjf Application November 6, 1935 Serial No. 48,481 a 13 Claims. (01. 33- 222) This "invention relates to direction indicating instrumentsand is particularly'concerned with a novel means of carrying or supporting the die rection indicating element of suchan instrument.

, The problem presenting itself in directional instruments such as compasses, turn indicators,

so that it will be influenced to'the least possible j offdirective instruments, most of which" include extent by forces other than the directing force, and-so that, when displaced from a true direction indication, itwill return quickly to-theftrue' direction. The prior" art shows numerous types mechanisms: requiring a high degree of precise machinework and adjustment to causethem to operate satisfactorily, resulting in high cost and a requirement of frequent adjustment and'calimum j f Objects of myinventionare (a) to provide a novel means ofimounting the directiveelement of an instrument, (b) to provide 'a'hydrostatically balanced fiuid suspension fora directive element, (c) to provide an instrument having a directive element suspended in a fluid medium of substantially equal specific gravity to the specific gr'avityloi the element, whereby mechanicalsupport for the element is unnecessary, '(d)' to pro vide an element ,hydrostatically suspended and out of direct contact with, a container filled with a fluid of appropriate density, (a) to provide a massive element hydrostatically suspended within a container for free movement relative thereto, (I) to provide a device according to (e) above, wherein a directive element is hydrostatically suspended within the massive element and is capable of damped, movement relativethereto, (g) to adjust the mass relationships of the several parts of theinstruments so as to eliminate undesired effects of forcesto which the instrument is not intended to be responsive, and (h) to provide certain means and structures to accentuate the action of an indicating element when same'is responding to those forces to-which it'is intended to be sensitive} s Further objects include the adaptation of various types of directive instruments, such as'bank', turn, inclinometer, horizon and others into .either separate or combination instruments, utilizing the hydrostatic suspension and mass adjustment principles of the invention. As the specification proceeds, it will become apparent that instruments according to .the invention may be easily. and reasonably fabricated, .and that the principles established will lend'themselves to a variety of other uses. Further objects will become ap- I parent also, with regard to details of construction of various embodiments of instruments by which their useis-made wholly'practicable. f K

In the drawings,'Fig. 1 is a section through a simple'form of instrument embodying :the principles oi thelinvention; j V

' Fig. 2 isa section through an instrument 011- ganized as a magnetic field direction indicator; Fig. '3 is a plan" of the'instrument of- Fig.- 2;

Fig. 4is a 'side elevation-ofthe instrument of Fig. 2;

Fig. 5 is a section through a panel mounting compass; a .1. Y 7

Fig. 6' is afront view of the compass of Fig. 5; Fig. 7 is a section through a panel mounting combination instrument embodying compass, bank horizon and accelerometer features;- i 8' is afront view of thexinstrument of Fig, 9 is a perspective view showingthe lens of the instrument of'Flgtfl c Fig. 10 is a plan of the accelerometer element; Fig. 11 is an enlarged fragmentary section of a portion of Fig. '7; and

Fig; 12 is a section through an; alternative structure adapted for use in an instrument of the type shown in Fig. 7.

.Fig, 1' represents a simple form of instrument illustrative of theprinciples of'hydr'ostatic suspension which I use. To make this principle cl'ear, let us assume a spherical container com-' pletely filled with any fluid. The fluid, filling the sphere, at all times moves bodily therewith,-

and translation of the sphere 1 in any direction will cause'no relative movementor displacement 'of the fluid molecules- Shouldthe sphere be rotated-the fluid, however, will not rotate bodily therewith, due to the inertia of its mass,(until high as well, there is a still greater resistance to rotation. Presuming that the sphere is started in uniform rotation, the outer layers of the 0011-. tained fiuidare first gradually set in motion, which motion is gradually transmitted ,to

the .3

whole fluid mass. If the sphere is subie'cted to} (I oscillating movement, only the outer layers of the fluid will-oscillate with the sphere, the central mass of the fluid remaining stationary.

Now. if a smaller sphere be contained concentrically within the larger one, the smaller sphere having a mass-volume, ratio exactly equal to the specific gravity of the fluid, the smaller sphere will act in a manner similar to the first assumed central fluid portion. Namely, the smaller sphere will not move relative to the container when the latter is translated, and the smaller sphere will lag far behind the container when rotation is imparted to thecontainer. Mathematical computations maybe set up to predict the time lag of the inner massive sphere and to obtain optimumlag conditions, taking into account the relative sphere diameters, moment of inertia of the inner sphere, viscosity and specific gravity of the fluid (the specific gravity being equal. for.

the inner sphere) and the inertia of the fluid as movement is progressivelyinduced therein from the rotating outer sphere inwards. The degree of lag of the inner sphere relative to the outer sphere is increased by a fluid of low viscosity, is

increased by an inner sphere having large moment of inertia, and isdecreased by a closerspacing of the outer wall of the inner sphere to the inner wall of the container. The relationship of sphere diameters then becomes important, and by'. evaluating the thickness of the'fluid layer with'respect to inner sphere diameter, it is generally found that an optimum lag condition is mal expansion and wide range of temperature betweenfreezing and boiling states, so that the instrument remains operative during all variations in climatic-temperature:

Methylene bromide, methyl iodide, ethyl bromide; carbon disulfide. i

In Fig. 1, I2 designates a spherical container of suitable material, such asglass. concentrically contained therein is a massivesphere l.3 having an outer diameter substantially less than the diameter of the container l2, the space 14 between the spheres being filled with a suitable heavy, non-viscous fluid. The sphere I3 then, is hy drostatically suspended 1 within the sphere l2. The sphere l3 contains a spaced concentric spherical indicating element l5, having a fluid l6 therewithin; another fluid l1 fills the space between the spheres I3 and IS. The element IS with its contained fluid has a speciflc'gravity the same as the fluid l1- The spheres l3 and I5, and the fluids land l1, together-are organized to have a specific gravity the sameas the fluid H.

The, sphere l3, then, will at all times move translationally in any direction with thesphere I 2,.without disturbing the concentric relationship, and the sphere l2 may move rotationally in any direction without disturbing the position of the sphere 1.3 except with'protracted unidirectional rotationof the'container l2. This latter condition would bemost infrequent in any normal service to which a'direction instrument might be subjected. Ordinarily, consecutiveunidirectional turns would seldom exceed one complete turn and most conditions would impose oscillating mover:

ment on' the sphere "which wouldnot aflect the] 1 sphere I i afl'all. The latter sphere should be made of a transparent material, such as glass,

which has aspecific gravity of about 2.5. The fluid in the outer space M may be of equivalent specific gravity, although a precise equality may be diflicult of attainment. Compensation, toattain equality when the fiuid'has a specific gravity V divergent from the sphere i3, is accomplished by filling the sphere IS with a fluid havinga specific gravity appropriate to effectthe desired hydrostatic balance. The directive element li gwhichf l may, for'inst'ance, have a compass needle l8,1s T .-simi1arly hydrostatically balanced within the 'sphere l3. The clearancebetween elements I3 and I5 is shown as being small, whereby a sub- V stantial fluid damping effect is induced between ,j

the elements; Since the element I3 is relatively a stationary, and sincethe directive element li is subject to movements induced by means other than forces affecting the element l3, this fluid damping eflfect makes the directive element "dead; bea reducing fluctuation and oscillatlon there of. If desired, thedirective element could in certain cases be directly attached to the sphere I 3.

Suitable indicia, are inscribed on the element 15, I

visiblethrough .the transparentspheres l2 and I3. The mass and specific gravity of thedirecti ve element areconsidered inv the design of the in! strument, to obtain the hydrostatic balance rev-.1

quired. I

-Figs..2, 3 and 4 show a I which essential devices for assembly and practical use havebeen incorporated. The directive-cle ment l5 comprises metalhemispheresfl joined by anexpansible annular diaphragm 12L fThe' compassneedle I8 is on a sphere diameter nor mal to the great circle formed by the diaphragm 2|, and a plurality oi. parallel perforatebamles 22 are. mounted within the sphere to,,damp,

a a... of mar-teat in I as I through the action of the fluid in the element .15,

tions which would tend to angularly displace the needle. l8. The massive element l3 comprises glass hemispheres 23 joined through afliiid-tight expansible annular diaphragm 24. Holes are movements of the element particularlyindirecprovided in the hemispheres 23, filled after S-embly h plugs :5, for mung the sphere, the fi t l5 having been assembled before joining the diaphragm 24 to the hemispheres. The as sembled sphere l3, with contained fluids and elements, isthen placed in the outersphere l2 com;

prising hemispheres 26 joined by a flexible toroidal diaphragm 21 which forms a mounting ring held by clips 28 ,swivelly mounted in the mounting structure 29. I H

Support pins 30, having small flatlieads 3|,or heads of other suitable shape, are mou'nted within the hemispheres 2 6 to h'oldthe sphere in con: centric relation during assembly. These pins are of minute sizeto reduce fluid friction, and the heads 3| provide a relatively frictionless support for the sphere l3, since, after assembly, the'outer course, that the specific gravity of materials-generally. vary with their temperature. It is, then,

'with the known. material characteristics, relatively. simple to proportion interior fluids and structures so that their aggregate specific gravity, when subjected to a finite temperature change,

varies in the same proportion as the specific grav- "ity of the suspending fluid when subjected to the same temperature change. The expansible diaphragms permit of expansion and contraction of the structures, the material of which generally would have lower coeflicients of. expansion than the fluids. g i v The instrument of Figs. 2, 3 and 4 comprises a magnetic field direction indicator. Suitable latitudinal circles are inscribed on theelement I 5, and likewise on the containing sphere l2. By aligning the respective latitudinal circles,'by angularly moving ,the sphere l2 in the clips 28 and by turning the sphere relative to the .mount 29, readings of angle of magnetic dip,,and bearing may respectively be taken from .suitable scales 32 and. 33,;inscribed on the annulus 21 and the mount 29, respectively. V

Figs. 5 and 6 showa compass builtaccording to the principles .of the invention, adapted. for panel mounting and direct reading. Here, the directive element 15 includes the expansible diaphragm 2|, and baffles 22 as in Fig. 2, but a pair of spaced parallel compass needles 5,! are utilized. The spacing R between the needles is such that the needles together have the same moment of inertia about any coplanare central axis. A small weight 52 is attached centrally in one of the hemispheres 20 to hold the great circle formed by thediaphragm 2| substantially horizontal, of!- setting the vertical component of thel'earth s magnetic field. To compensate the weight 52 in I order that hydrostatic balance may be maintained, an'empty cup 53 is attached centrally of the upper sphere 20. The element l5, though hydrostatically stable, will be responsive ,in its absolute position relative to the horizon, to resultant forces acting through the center of the instrument. When static then, the diaphragm will lie in a horizontal plane, but when used, for instance, in aircraft which are subject to other forces dueto maneuvering, the element, I! will act as 'a bank indicator, the diaphragm taking a position corresponding. toa normal to. the resultant forceacting on the aircraft. This indication, in a properly executed turnjwill maintain the indicator in the same relation to the instrument casing as when the craft isinlevel, uniform flight; Theinstr'ument also serves in some degree as a horizon or angle of climb indicator, although its indications inthese functions would onlyibe trustworthy where any acceleration forces acting on the instrumentare of very low magnitude, since the position indicator is responsive,

in its angular position, to radially applied forces acting thereon which in aircraft, are frequently of a magnitude approachingor exceeding the force due ;to gravity. V

When the indicator [5 is moved by variable forces (other than gravity and the force due to the earth's field acting on the compass magnets), the frictional .drag between the indicator. l5 and the massive sphere l3- will tend to rotate the latter; the mass of sphere l3 will resist 'such movement to damp movement of the indicator.

.If slight motion is imparted to the sphere l3,

it will tend to rotate beyond the new statically balanced state, tending.,to slightly overcontrol the indicator. Upon return of the indicator to normal, due to normalization of the forces acting thereon, the massive sphere will be stopped due 'phragm 56. A stout ring 51 is soldered or welded to the front of the truncated hemisphere 55, the diameter thereof being great enough to permit entry of the sphere IS. A concavo-convex lens completes the spherical form of the' sphere l2, and a wire lubber line 58 is clipped between the lens and the ring 51. A union ring 59 and suitable packing 60 complete the lens joint. The whole instrument 'isjpreferably, mounted in felt or sponge. rubber 6| carried in a housing 62 adapted'for panel attachment by a ring 63 and screws 64. I f

Figs. 7 through 12 show aninstrument, and parts thereof, embodying certain novel principles in additionv totho'se'already described. This instrument, is particularly adaptable for aircraft, and coordinates into one easily read device functions previously requiring thefus-e of no less than four separateinstruments, namely, a stable di-' rectional compass, an artificial horizon, a bank indicator, and an accelerometer. The one instrument thus gives all the information necessary to ascertain the attitude of an aircraft in blind or instrument fiying. Although the general principles of construction and operation are essentiallythe same as previously described, the structures involved are different. An outer container, having, a spherical interior surface, is composed of a hemispherical shell" and a truncated shell H joined to the shell Ill through an expansible annular diaphragm I2 and a flange connection 13. A concavo-convex lens 14 is suitably joined to the front 'of the shell II by a bezel 15, a flange 16 formed at the front of the shell 1| serving for mounting the instrument on a panel 11.

Closely spaced within the composite container is a shell I! of glass, Celluloid or other single or composite transparent material having an appropriate specific gra ty. The shell comprises two hemispheres joined long a great circle as at 19, the joint being organized to provide an acceler ometer 80, described later indetail. A port 8| is formed in the top hemisphere, and a weight 82 is attached to-the bottom hemisphere diametrically opposite the port; This shell is relatively light, so far as rotational moment of inertia is concerned, and when 'hydrostatically balanced within 'the container, is responsive to resultant radially acting forces imposed on-tlieaircraft, thus serving "as a bank indicator. The great circle formed by..the juncture of the hemispheres provides an index read with reference to horizontaland .vertical lubber line 'sets83 and 84 inscribed, respectively, on the inner" and outer sur-- faces of the lens H. The accelerometer com prises a band 85, preferably black, circumscribing the joint [9 and mechanically reinforcing same, a spring ring 85, and a movable ring 81. The

' of the red band 88. The'springs may be adjusted to cause a redband showing proportional to the" number of gravity force factors imposed thereon, or may be adjusted to hold the red band invisible until a specificnumber of gravity forces have been exceeded. For instance, an aircraft designed to g acceleration may have its instrument adjusted to show red at 8 g acceleration.

Support wires 99 with headed ends are appropriately spaced within the shell 18 to support,

during assembly, a concentric, relatively mass'ive, sphericalshell 9|, upon Which are inscribed an equatorialgreat circle 92 and a plurality of normal great circle arcs .93. This shell is vented at 94, and comprises hemispheres joined along the great circle 92 and clamping between them, at the joint, a spherej95 which is'located eccentrically 'relative to the shell 9|. This sphere 95 comprises halves 96 and ,9'| with flexible flanges 98 clampe'dbetween the halves of the shell 9|, to provide an expansion diaphragm. The upper half 91 is provided, with opposed bearings 99 supporting a spindle l'flflon which is mounted a compass magnet |9|. By the spindle mounting, the magnet may find its own inclination in the earth's field without exerting a tilting force on the sphere 9|,,butwill tum the sphere 9| in azimuth to form a true reading directional instrument. By virtue of the fluid mounting and hy-j drostatic balance, thesph'ere 9| will not be ap-, preciably displaced by any ordinary maneuver of theaircraft, and willgive a true reading'at all times; though in certain attitudes of the craft an accurate directional reading will be diificult, such a reading may easily be made as soon as the craft regains a reasonably level attitude.

The lower, outermost half 96 of the eccentric sphere 95 is provided with a conical depression I02 the sides of which are tangent to the sphere. A ball [03' is placed within the sphere for free movement therein except as such movement is damped by the fluid within the sphere. A counterweight I04 is arranged diametrically opposite the depression Hi2, or alternatively, the top half 91 of the sphere may be of greater thickness or of heavier-material than the lower half 96, so that the assembly comprisingsphere 95 is exactly balanced about the center of the sphere 9|. Like wise, means will be provided to effect coincidence of the center of buoyancy with the center of the sphere 9|. Thus, with the ball I03 omitted, the center of gravity, and the center of buoyancy will be coincident with the center of sphere 9| When the ball is assembled and is lying in the depression I02, the assembly will tend to remain in the upright position shown. The function of the ball-and eccentric sphere is to right the sphere 9| gradually should it become rotationally displaced from an upright position and yet, not to provide a fixed eccentric weight which would tend to" move the sphere 9| appreciably when it is subjected ,to lateral acceleration forces. When accelerations having a horizontal force component are imposed on the instrument, said horizontal component, if. of sumoient magnitude,"

will move the ball out of the'conical depression and along the eccentric sphere surface without substantially rotationally displacing the sphere 2,192,143 i g H 9|; When the horizontal forceceases or changes direction, the ball will roll alongthe sphere'surface without appreciably effecting sphere rota-: 1

tion. Should a horizontal force componentlast: an appreciable length of time, the ball will proportionately press against the spheresurface which, by virtue of the sphere surfaceeccen tricity, will cause an unbalanced rotational force on the sphere, eventually turning it so that the.

depression I02 with the ball therein, will'event-j' ually become aligned with the 'direction-offac :v tion of the acceleration force.

ball I03 will be very light so that'a force would have to be applied over a period of several minutes to alignthe sphere poles 'with'the' force'direction. Thus, in any flying at all likely to be.

encmnteredthe only acceleration force acting in one direction for a protracted period is that" of gravity, so that the spherell will always tend However itis intended that the'sphere rotating effect of the to stay in, or return to, a position'whereirl the;

poles thereof are-'aligned'on a normal to the. earth's surface. sphere p'rovidea means for righting the sphere due to a steadily-imposed force and for mini-' mizing overturning of thesphere due to strong other forces of short duration. The sphere9l e 10058 ball an eccentric,

is, as shown, widelyspaced from-the sphere l8 and has a considerable rotational inertia;'wh'er'e 3 by the sphere l8 m'ay'move freely around the sphere 9| without moving the latter. The sphere 9| is preferably made from material ofhigh specific gravity,- the' hydrostatic balance thereof,

in the surrounding fluid, being compensated by the use of a fluid of low specific gravity within the eccentric sphere 95. 1 l

Fig. 12 shows an alternative construction which may replace the contents of the s'pherell, the

alternative providing an improved construction to compensate overturning tendencies of" the sphere induced by fluid drag caused by rapid movements of the sphere". Herein, apair of similar half shells I20 are clamped inopposed relation between the halves of the sphere 9| These shells have a special cam shape increasing in radial distance from the sphere ceritery-from a; certain minimum distance at'the sphere edua tor to a maximum distance in alignment with the sphere poles. "With a fluid within the shells I29 different in specific gravity from the fluid without the shells, the center of buoyancy isv maintained coincidental with the sphere 9| due to the symmetry of the shells. Now,"a' special 'cam' shell I 2| is attached at "its; circular edge along the sphere equator and is formed so as to-have a constantly diminishing radial distance from said equator to the upper pole, as measured to the sphere center. The shell |2| and the lower shell |20, then, together form a substantially:-

heart-shaped cam upon which the free ball I22 may travel. Likewise, the shell I 2|, considering ter of. gravity of, the assemblage willbe slightly below the center of the sphere 9|, that is, toward the depression 123 I ,V y,

Inoperation, assume that an acceleration force is imposed on the instrument from .left to right.

arcane turn counterclockwise byvlrtue of its high center 'of gravity when the ball is not acting. Thus, the fluid drag turning effect is compensated by a counter turning-effect in the sphere 9|. Ordinarily, the aircraft and instrument will shortly return to equilibrium, and .the ball will vroll back to the depression I23. Should the horizontal force be continueddn one direction for a long period, the ball I22 will eventually turn. the sphere 9i to the position .whereat itspoles are alignedwith the resultant force. Should such an'upset occur, even to the extent where the sphere is overturned so that theshell l2l is at the bottom and the shell I ontop, the'ball :willact on the cam surfaces ofathese shells to "eventually right the sphere, even though the sphereis overbalanced statically; This effect is produced by the shape of thecam surfaces and the action of the ball thereon, the ball always exerting a force'tending to turn the sphere until the-ball reachesthe depression 122. .It willbe noted that the'apex of the shell III is inturned,

to prevent the ball ever reachingv a static dead center" position should the sphere come to rest 180 out of-normal position. This apex may conventionally be provided with an oriflcel to permit of fluid pressure equalization throughout the interior of the two shells I20. I

In this embodiment, paired, spaced compass magnets l2! are carried on a spindle I26 borne at itsends in spindle bearings I21 carried adjacent the periphery of the shell III}? Fluid vents I are formed in the sphere 9], whereby temperature changes are assumed by the joint between the shells I20. Theplug in. the top shell I20, and the orifice l in the shell l2l, provide means for assembling the ball I22 as well as fllling the shells with fluid. Another alternative construction contemplates forming the halves of the massive shell 9| with the interior cam faces as part thereof, rather than using the separate shells III and III.

While I have described my invention in detail in its present preferred embodiment, it will be obvious to those skilled in the art, after understanding my invention, that various changes and modifications may be made therein without departing from the spirit or scope thereof. I aim in the appended claims to cover all such modifications and changes.

What is claimed is:

1. An instrument comprising a plurality of at least three concentric hollow spheres at least two thereof each hydrostatically suspended one within the next outersphere, and fluids filling thev several inter-sphere spaces eachhaving a specific gravity equivalent to the a gregate mass-volume ratio of the within spheresand fluids.

2. In an indicating instrument, a spherical support, a transparent spherical primary element of high inertia, hydrostatic means for supporting said primary element in said support for unlimited rotation in all directions with respect thereto with substantially no transfer of kinetic energy therebetween, a secondary sphericalelement of low inertia closely spaced within said primary element, and hydrostatic means for supporting said secondary element within said primary element for unlimited rotation in all directions with respect thereto and with a substantial transfer of kinetic energy therebetween.

3.'An indicating combination instrument including, in combination, apluralityof concentric spheres separated by fluids each of whose density is equivalent to the mass-volume ratio of the containedspheres and fluids, said spheres being relatively movable according to the degree of damping'imposed thereon by fluid friction, one

said sphere having a directional element having a force component adapted to urge said sphere to a definiteposition about a vertical axis and I being adapted by its mass and free suspension to maintain an index thereon in a flxed attitude,

and another of said spheres having a weight eccentric to the sphere center organized to turn the sphere in the direction, of externally imposed forces.

- 4. A bankindicator and compasscomprising a first spherical memberhaving a transparent portion, a second thin wall spherical member within .and closely spaced relative to the first member and having an eccentric center of -gravity for. normally maintaining said second sphere in align- I ment with a resultant radial force imposed thereon, and a third spherical member of relatively thick wall and high-rotational inertia widely spaced withinsaid second sphere, each said sphere being hydrostatically balanced within the next outer sphere by fluid within the inter-sphere spaces, each fluid having a specific gravity respectively equivalent to the mass-volume ratio of the suspended sphere and its contained elements.

5. In an indicating :instrument, a container element having a smoothly spherical interior surface, a fiuid substantially filling said container, an elementimmersed in and supported by said fluid free for unlimited rotation in any direction relative to the container element, the surfaces of said element being widely spaced from the interior surface, of said container element, and deformable resilient filaments attached to one said element and extending nearly to the other said element, and lying along lines radiating from the center of said elements, said filaments being of such minute thickness as to cause a minimum of fluid friction between the elements and fluid upon relative motion thereof while serving to centralize one element with respect to the other.

6. An instrument comprising a plurality of concentric hollow spheres each hydrostatically sustained one within the next outer sphere, and fluids filling the several inter-sphere spaces each having a specific gravity equivalent to the aggregate mass-volume ratio of the contained spheres and fluids, the several spheres of the assembly being provided with expansible means to permit change in the volume thereof upon temperature changes in proportion to the expansion of contained elements and fluids, by which the weightvolume ratio of each fluid and its contained sphere is proportionally maintained throughout said temperature changes.

'7. A-device including in combination, a container having a smoothly spherical interior surface, a fluid substantially fllling said container therein, said container being adapted to rotate at least a complete revolution about said member in any direction without disturbing said member.

8. A direction indicator including a fluid-inimersed substantially closed movable member having an axis of gravitational stability, a magnet pivoted within said member about an axis fixed relatively thereto to rotate in a plane parallel to or including said axis and automatically to align the magnet poles with the dip and azimuth of the earth's magnetic field, and means for automatically adjusting the buoyancy of said member, including a fluid-tight expansible container within said member and having a liquid enclosed therein.

9. A combination flight instrument for aircraft comprising a relatively'massive hollow sphere, a cam surface formed therewithin, a weight freely movable over said cam surface normally'tending to urge said massive sphere, by influence of gravity on said movable Weight, to a predetermined attitude with respect to the vertical, a magnet carried by said massive sphere forming a directive element therefor, said sphere having indicia on the surface thereof, and fluid me'ans holding said massivev sphere in hydrostatic suspension forfree movement under the influence of said weight and magnet;

' 10. Acombination flight instrument for aircraft comprising a relatively massive hollow sphere, a cam surface formed therewithin, a Weight freely movable over said cam surface normally tending to urge said massive sphere, by influence of gravity onsaid movable weight, to a predetermined attitude with respect to the vertical, a magnet carried bysaid massive sphere forming a directive element therefor, said sphere having indicia on the surface thereof, and fluid means holding said massive sphere in hydrostatic suspension for free movement under the influence of said weight and magnet, said magnet being pivoted 'to permit dipping thereof relative to the sphere without imposing a vertical twistin couple on said massive sphere.

11. An aircraft flight instrument for indicating a pre-set course including, in combination with a transparent spherical. support, a dip magnet within said support having free universal rotation with'respect thereto, a spherical shellwithin said support and connected to said dip magnet and bearing a set of parallel indicia at intersections of its surfacewith imaginary spaced parallel planes normal to the polar axis of said magnet,

a second set of similar indicia upon saidsupport,

and means mounting said support for movement about two mutually normal axes to obtain paralf, lelism of the two sets of indicia for any given orientation of the aircraft. V

e 12. In an attitude indicating flight instrument for aircraft having an elongated index having its principal dimension disposed in a plane substantially normal to the direction of strong acceleration'forces to which the instrument is subjected, a weight in the form of a narrowstrip parallel to and adjacent to said index, and, spring means supporting said weight, said means being of such strength as to be compressed by said weight at a given dangerous rate of acceleration of the aircraft, thereby constituting a warning-signal byrelative parallel translation betweensaid index and strip. ,v q

13. In an indicating instrument, in combination, a pendulous member freely supported within a housing, said housing being free for u n-. limited movement in any rotational sense relaobserving .the position ofthe member relative thereto, an index on said member comprising relatively movable bands positioned in parallel member I .30 tive to the member, a window in said housing for 

